Sucralose is conventionally prepared by chlorination of a sucrose-6-acylate in the presence of a tertiary amide such as dimethylformamide (DMF) to form a mixture of chlorinated sucrose-6-esters, the largest component of which is 4,1′,6′-trichloro-4,1′,6′-trideoxy-galactosucrose-6-ester, followed by quenching at high pH, after which the DMF is removed and the acylate is hydrolysed to form crude sucralose prior to purification.
DMF is thus useful as both a solvent and a reactant during chlorination. However, cost effective manufacture depends upon recovery of this solvent from a number of streams, even when it has decomposed directly or indirectly to DMA. This recovery is economically important because of the cost of DMF and the fact that for every mole of sucralose produced, 2-20 moles of may ultimately be converted to DMA. Therefore, recovery of the solvent is very important to the economics of the process. It is also undesirable to harm/inhibit a biological waste treatment system by exposure of biomass to high levels of DMA.
It is known art to react DMA with CO under non-aqueous conditions with sodium methoxide catalyst to restore DMF. Therefore, safe and economic recovery of DMA can be used to replace costly DMF destroyed in sucralose manufacture.
The DMA is purified and concentrated by distillation and reacted with CO to reform DMF for recycle to main DMF purification systems. The separate solvent free carbohydrate waste streams can then be neutralized and treated biologically without interference by solvents.
In the case where DMA contaminates desired carbohydrate streams, careful choices must be made to preserve the carbohydrate while still freeing volatile DMA by addition of strong base, thus allowing distillation of the DMA. Where the DMA is in the presence of desirable carbohydrate, reactions can occur such as the preferable deacylation as well as undesirable decomposition of sucralose. It is thus desirable to remove and recover DMA but at the same time it is desirable to maximize the yield of sucralose by minimizing the formation of side products.